Fire-retarding coating



ma mals Patented Oct. 30, 1945 UNITED STATES PATENT OFFICE No Drawing.Application July 21, 1943 Serial No. 495,572

(Granted under the act of March 3, 1883, as amended April 30, 1928; 370O. G. 757) 1 Claim.

This application is made under the act of March 3, 1883, as amended bythe act of April 30, 1928, and the invention herein described, itpatented, may be manufactured and used by or for the Government of theUnited States of America for governmental purposes without the paymentto me of any royalty thereon.

This is a continuation in part of my copending application for patent,Serial No, 452,765, filed July 29, 1942.

I hereby dedicate the invention herein described to the free use of thepeople in the territory of the United States to take effect on thegranting of a patent to me.

This invention relates to coating preparations for application to thesurface of a combustible material such as wood to increase its fireresistance.

Aqueous solutions of fire-retarding chemicals are known, one or twocoats of which will afford some protection. However, their viscositiesare substantially no greater than that of water, and their solubility islimited. Many ,coats are, therefore, necessary to give protectionagainst fires of a moderate or higher degree of severity. For example,the maximum concentrations of either of two of the best fire-retardants,monoammonium phosphate or dianimpnium phosphate, at 70 F., are 27 and 1grams grams of solution, respectively. These, when applied by brush tosoft woods, give coatings of approximately 1.5 and 3.0 grams,respectively of the dry chemical per square foot of surface. Laboratorytests have shown that approximately 20 grams of ammonium phosphate persquare foot are necessary for protection against fires of moderateseverity. Therefore, a large number of coats of the solution arenecessary for good protection, and use of the solution is not practical.

An object of this invention is to provide a fireretarding coatingpreparation of such nature that good protection is obtained byapplication of a few coats, and which is of low cost, and may beprepared from readily obtainable constituents. In particular, an objectis to provide an aqueous solution of fire-retarding chemicals of suchhigh viscosity and high content of fire-retarding chemical that enoughfire-retarding chemical can be applied in one or two coats tosubstantially check flame spread. A further object is to provide a newfire-retarding coating preparation that consists essentially of activefire-retarding ingredients, with a minimum of combustible ingredients.

I have discovered that by using a suitable thickening agent in thefire-retarding preparation, it is possible to apply grams or more of thedry material per square foot in one coat. Soluble alkali alginates, suchas sodium and ammonium alginates, are examples of satisfactorythickening agents for this purpose. These have the property of producingvery thick gels with as little as 2 per cent by weight of the alginatedissolved in water. These gels do not act chemically with fire-retardingchemicals containing ammonium, alkali metal or magnesium ions, andtherefore they may be used with these. An exception is borax (sodiumtetraborate) which reacts with sodium and ammonium alginate solutions tocause them to set to a rubbery gel. Borax may be used as a constituentof a fire-retardant alginate preparation, however, if sufficient boricacid is mixed with it to prevent setting. By means of these alginates,the viscosity of the preparation is so increased that it is possible toadd much more fire-retarding chemical than necessary to saturate thesolution, and a thicker coat o the preparation may be applied to thesurface.

I have also discovered that including in the preparation an amount ofpulverized fire-retarding chemical in excess of that required tosaturate the aqueous solution prevents formation of large crystals inthe coating. This insures a uniform coating of small crystals.

I have further discovered that other materials, such as china clay andbentonite, may be introduced to improve brushing qualities, to stabilizethe solution against settling, and to further thicken it.

Other materials such as wetting agents, decay and mold preventatives,corrosion preventatives, and coloring agents may also be added.

The relative proportioning of ingredients may be varied, and a widevariety of characteristics may be obtained by changing the proportions.The following examples of highly satisfactory proportions are given byway of illustration.

Example 1 Parts by weight Monoammonium phosphate 60 2 percent aqueousalginate gel 40 The alginate gel is prepared by stirring 2 parts byweight of sodium alginate into 98 parts of hot water. The 60 parts ofmonoammom'um phosphate are ground in a pebble mill with the 40 parts ofgel until the monoammonium phosphate is reduced to a fine state ofsubdivision; or the M, ll.

monoammonium phosphate may be added in prepowdered form.

Example 2 Parts by weight Monoammonium phosphate 48 China clay 12 2percent aqueous alginate gel 40 The gel is prepared in the same manneras in Example 1. The proper proportions of monoammonium phosphate andchina clay are ground together, and this mixture is milled or mixed intothe gel.

Example 3 Parts by weight Borax (Na2B4Om10H2O) 30 Boric acid 30 2percent aqueous alginate gel 40 The gel is prepared in the same manneras in Example 1. The proper proportions of borax and boric acid areground in a pebble mill with the 40 parts of gel until the particles ofsolid are reduced to a fine state of subdivision.

The high viscosity of these preparations maintains the excess of finelyground fire-retarding chemicals in suspension during application of thecoating. Although the chemicals may settle upon standing, they remain ina finely divided state, and are readily returned to suspension bystirring.

Both of the first two above examples employ monoammonium phosphate asthe fire-retarding chemical, and the third example employs borax. Theseare the most effective from the standpoint of fire-retardingcharacteristics, resistance to dampness, and production of viscosity.Other chemicals may be used, however, such as ammonium sulfate,diammonium phosphate and ammonium sulfamate. All that is necessary isthat a chemical be selected that does not react with the alginate.

The preparations of this invention are especially valuable for interioruses, such as for coating walls and ceilings of attics, storage sheds,warehouses, barracks, hangars and any other buildings of Woodconstruction. The Water solubility of the principal ingredient makesthem unsatisfactory for exterior exposures. Their fireretardingefiectiveness is excellent, and insofar as at present known, ispermanent under dry conditions. The preparations are simple to compound,either by manufacturers or home owners, and are simple to use.

Having thus described my invention, what I claim is:

A fire-retarding composition comprising an aqueous solution of an alkalialginate of about 2 percent by weight concentration having finelydivided bo andboric acid incorporated therein in the proportion oPaboutparts of the gel, 30 parts of the borax and 30 parts of the boric acid,said composition being such that one application of the composition on awood surface upon drying will yield a coating Weighing at least 10 gramsper square foot and having at least percent of active fire-retardingchemicals.

ARTHUR VAN KLEECK.

